Toxoplasma gondii is an important opportunistic infection of AIDS patients. Improved strategies and approaches are urgently needed to more effectively prevent and treat recurrent infections in AIDS. Following primary infection, a chronic life-long T. gondii infection characterized by the presence of persisting cysts containing slowly or nonreplicating bradyzoite parasite forms is established in CNS/brain. Reactivated infection due to cyst rupture during immune suppression causes a difficult to treat and life-threatening Toxoplasmic encephalitis in AIDS. Currently, no vaccine is approved for use in humans to prevent infection and drug treatments for acute infection are suboptimal. Eradicating pre-existing cysts and chronic infection is an excellent approach to control/prevent infection in AIDS. However, no current treatment is effective at eradicating pre-existing cysts and chronic infection. Lack of progress in targeting cyst stages can be attributed to major gaps in our knowledge of parasite biology underlying cyst development and maintenance of chronic infection. Recent progress in understanding the complex host-parasite interaction has revealed that many rhoptry bulb (ROP) proteins appear to be central players in host cell manipulation due to their secretion into the host cell at invasion and their subsequent localization to host cell cytosol/nucleus or their intimate association with the parasitophorous vacuole. Host cell manipulation by these secreted ROP proteins is likely to be critical to the success of parasite biology necessary for acute and chronic infection in vivo. The parasitophorous vacuole appears to be critical for replication of tachyzoites as well as being central to the development of the cyst wall and tissue cyst that characterize chronic infection. We hypothesize that a family of ~ 34 secreted ROP proteins possessing homology to kinases (the ROP kinome) are outstanding candidates as potential targets to disrupt virulence, cyst development, or chronic infection. Here, we propose to delete each predicted gene member of the secreted ROP kinome in type II T. gondii, and to then ascertain any defect in acute virulence, in early cyst development, or in chronic infection. Using a directed functional genetic approach, this work will identify specific members of the secreted ROP kinome that participate in critical functions required for establishing or maintaining chronic infection in vivo. This project will identify and validate specific secreted ROP kinases as key targets for preventing acute or chronic infection. This project will also develop essential tools and methods required for the future undertaking of larger scale higher throughput knockout and functional genomic projects in type II T. gondii. Consequently, this innovative project has high overall impact by advancing genetic models for dissection of type II biology, by revealing new aspects of host-parasite interaction, and by exposing new targets to prevent or eradicate chronic infection.